Global Load Balancer Calculator
Derive failover time from health-check interval, failure threshold, DNS TTL and draining, and price the DNS queries.
About Global Load Balancer Calculator
A global load balancer cannot react faster than interval × threshold, because it deliberately waits for consecutive failures to avoid ejecting an endpoint over one dropped packet. After the decision, clients keep using the old answer until the DNS TTL expires and existing connections finish draining, so the DNS TTL is usually the largest single term. Tightening the health check without lowering the DNS TTL barely improves real failover time while multiplying probe traffic against every endpoint. Query pricing and per-endpoint monitoring fees vary by provider, so confirm the current rates before you size the pool.
Formula
Global Load Balancer
detection = health-check interval × failure threshold; convergence = decision propagation + DNS TTL + connection draining; total failover = detection + convergence.
- detection
- Time before the balancer decides an endpoint is down
- convergence
- Time before every client is actually using a healthy endpoint
- failure threshold
- Consecutive failed checks required, which suppresses false positives
Worked example
With the default values below, Global Load Balancer Calculator returns Total Time to Fail Over of 85.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Health-check intervalaccepts 1–300 seconds
- 10 seconds
- Consecutive failures before ejectionaccepts 1–10 checks
- 3 checks
- Decision propagation to the edgeaccepts 0–600 seconds
- 5 seconds
- DNS TTL on the load-balanced recordaccepts 0–86,400 seconds
- 30 seconds
- Connection drainingaccepts 0–3,600 seconds
- 20 seconds
- Failover events per monthaccepts 0–1,000 events
- 1 events
- Endpoints in the poolaccepts 1–1,000 endpoints
- 6 endpoints
- Locations running the health checkaccepts 1–200 locations
- 4 locations
- Authoritative DNS queriesaccepts 0–1,000,000 million/month
- 120 million/month
- Price per million DNS queriesaccepts 0–100 USD
- 0.6 USD
- Monthly fee per monitored endpointaccepts 0–10,000 USD
- 1.5 USD
Results
- Total Time to Fail Over
- 85.0 seconds
- Detection Time
- 30.0 seconds
- Convergence Time
- 55.0 seconds
- Monthly Downtime From Failovers
- 1.42 minutes
- Availability Lost to Failovers
- 0.0033%
- Health Checks per Minute
- 144
- DNS Query Charge
- $72.00
- Endpoint Monitoring Charge
- $9.00
- Monthly Cost
- $81.00
Step by step
- 1Values used
- 2Global Load Balancer
- 3Total Time to Fail Over= 85.0 seconds
- 4Detection Time= 30.0 seconds
- 5Convergence Time= 55.0 seconds
- 6Monthly Downtime From Failovers= 1.42 minutes
- 7Availability Lost to Failovers= 0.0033
- 8Health Checks per Minute= 144
Assumptions and limits
- The result is derived only from the 11 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Global Load Balancer calculated?
detection = health-check interval × failure threshold; convergence = decision propagation + DNS TTL + connection draining; total failover = detection + convergence. A global load balancer cannot react faster than interval × threshold, because it deliberately waits for consecutive failures to avoid ejecting an endpoint over one dropped packet. After the decision, clients keep using the old answer until the DNS TTL expires and existing connections finish draining, so the DNS TTL is usually the largest single term.
Why does Global Load Balancer matter?
Tightening the health check without lowering the DNS TTL barely improves real failover time while multiplying probe traffic against every endpoint. Query pricing and per-endpoint monitoring fees vary by provider, so confirm the current rates before you size the pool.
What values do I need to enter?
This calculator takes 11 inputs: Health-check interval, Consecutive failures before ejection, Decision propagation to the edge, DNS TTL on the load-balanced record, Connection draining, Failover events per month, Endpoints in the pool, Locations running the health check, Authoritative DNS queries, Price per million DNS queries, Monthly fee per monitored endpoint. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why not set the interval to one second and the threshold to one?
Because a single lost probe would then eject a healthy endpoint, and with several probe locations against every endpoint the check traffic itself becomes significant. Consecutive-failure thresholds exist to trade a few seconds of detection time for far fewer false ejections.